To be able to test system calls, syzkaller needs descriptions of the system calls for each target OS. The descriptions are stored in .txt files inside the sys folder of syzkaller. For FreeBSD the folder is <syzkaller>/sys/freebsd/. Modifications of these files require three steps in order to integrate it into syzkaller.

Step 1: Generate .const files from .txt files.

This requires FreeBSD source files on the host. I copied them to ~/freebsd/usr/src.

make extract TARGETOS=freebsd SOURCEDIR=~/freebsd/usr/src

Step 2: Generate Go code for syzkaller based on the .txt and .const files

This requires clang-format. If not already installed

sudo apt install clang-format

After that, run

make generate

Step 3: Build syzkaller on host and syz-executor on FreeBSD VM

See